Alpine insects: physiology and evolution in cold, thin air

Abstract:

The dramatic environmental changes that occur along an altitudinal gradient and the harsh living conditions at high altitude profoundly affect the evolution and physiology of organisms. Organisms living along a mountain must possess specialized adaptations to succeed in their local environment or else, they must be able to succeed in a wide range of conditions. In Chapter 1, I use weather balloon data to characterize the high altitude environment, and then review the literature to explore how these physical changes may affect the physiology and evolution of insects. In Chapter 2, I present data from a comparative study on patterns of intraspecific insect body size across altitudinal gradients. The probability that intraspecific body size will increase or decrease along a mountain is influenced by the life history and environment of the species. In Chapter 3, I explore both the direct and interactive affects of air density and temperature on the feeding rates of larval Drosophila melanogaster. Feeding rates were slower at low temperatures and in hypoxia. In Chapter 4, I ask how beneficial plasticity may help flying insects cope with cold environments. Cold temperatures cause increased flight failure and reduced motivation to fly. However, D. melanogaster reared in cold temperatures are better able to initiate take-off flight at cold temperatures than flies reared at warm temperatures. The primary mechanism that improved flight performance in cold temperatures was reduced wing-loading. In Chapter 5, I study the evolutionary limits of adaptation to cold environments. For ectotherms, biological processes slow down as temperatures get colder. However, it was unclear whether insects that have evolved in cold environments are able to evolutionarily compensate such that their biological rates match those of warm-adapted species (biochemical adaptation hypothesis). According to a phylogenetically controlled comparative study, cold-adapted insects have much slower rates of population increase than warm-adapted insects, suggesting that thermodynamics, more than evolutionary compensation, establishes maximum population growth rates.